Ultrapure water has a wide variety of uses, such as cleaning electronic components and surface treatment. In recent years, demands for a small amount of high-purity ultrapure water to be used as cleaning water or water for immersion exposure have been increasing.
Typically, when high-purity ultrapure water is supplied to a use point, the quality of ultrapure water to be supplied is monitored from various aspects using multiple on-line measuring instruments so that whether or not the purity is maintained can be constantly monitored. Examples of the measuring instruments used at this time include a resistivity meter, a particle meter, a dissolved gas concentration meter, a TOC meter, a hydrogen peroxide concentration meter, a silica meter, a boron meter, an evaporation residue meter, and a water temperature meter. The measuring instruments are selected depending on monitoring items required for its use (for example, see Patent Document 1).
FIG. 2 is a system diagram showing a conventional ultrapure water production facility provided with a plurality of measuring instruments for monitoring the water quality. Raw water (for example, primary pure water) introduced from a pipe 10 is supplied to an ultrapure water production system 2 via a storage tank 1 and a pipe 11, is raised in pressure by a pump in the ultrapure water production system 2, and is treated by various polishing-up mechanisms (such as TOC removal, degassing, dissolved ion removal, and particle removal). Thus, ultrapure water is produced. The ultrapure water produced in the ultrapure water production system 2 is supplied to a use point 3 through an ultrapure water supply pipe 12 to be used. At this time, in order to maintain the purity of the ultrapure water, a circulation system is formed in which an amount of ultrapure water larger than the amount used in the use, point 3 is supplied, and unused ultrapure water is returned to the storage tank 1 through an ultrapure water return pipe 14 to be reused as the raw water.
A portion of the ultrapure water supplied from the ultrapure water production system 2 to the use point 3 is extracted by a monitoring water extracting pipe 13 branching off from the pipe 12 and is introduced into the respective measuring instruments arranged in parallel (in FIG. 2, a particle meter A, a resistivity meter B, a boron meter C, a DO/DN (dissolved oxygen/dissolved nitrogen) meter D, a silica meter E, a TOC meter F, an H2O2 (hydrogen peroxide) meter G, and an evaporation residue meter H), where predetermined water quality items are measured. The monitoring wastewater after the measurement is discharged from the respective measuring instruments A to H to the outside of the system through a monitoring wastewater discharging pipe 15.
As shown in FIG. 2, the quality of ultrapure water is independently measured by these measuring instruments. Therefore, ultrapure water, serving as monitoring water, is introduced from the extracting pipe 13 into the respective measuring instruments, and the monitoring wastewater after the measurement is discharged from the respective measuring instruments.
The amount of monitoring water required by each of these measuring instruments for measurement is only several tens to several hundreds mL/min. However, the larger the number of monitoring items, in other words, the more the high-purity ultrapure water is required, the larger the number of monitoring measuring instruments. As a result, the total amount of monitoring water required for water quality monitoring increases. Therefore, in the case where a small amount of high-purity ultrapure water is used, the amount of monitoring water can be larger than the amount of ultrapure water supplied to the use point. In such a case, in order to ensure the amount of monitoring water, the ultrapure water production system needs to be made larger than required for the primary use. This has lead to an increase in the system cost.